1. Field of the Invention
The present invention relates to a method and apparatus for cooling intake air prior to entry into a combustion chamber of a boosted internal combustion engine, particularly, although not exclusively, for use in a diesel engine.
2. Description of Prior Art
Many automotive engines are boosted by compressing air prior to admission to internal combustion chambers. A turbocharger includes a turbine wheel that is driven by the exhaust gases from the engine and which in turn drives a rotary compressor. A supercharger includes a rotary compressor which is directly driven by the engine or by a motor which is ultimately powered by the engine. Diesel engines in particular are predominately turbocharged in order to increase the power of the engine.
When incoming air is compressed, it is simultaneously heated. Conventionally, the intake air is cooled by use of a charge air cooler or intercooler prior to admission to the combustion chamber.
Often such a cooler is a bypass passage so that the charge air can bypass the cooler, for example to aid engine warm up, to reduce emissions or to reduce combustion noise. The charge air is admitted to the bypass passage via a bypass valve which is controlled in accordance with various engine operating parameters. Use of a bypass passage is particularly relevant for diesel engines which usually have a charge air intake passage which is not controlled by a throttle valve in dependence upon an accelerator position.
However, a problem with such known intake air systems is that the bypass valve can malfunction and remain in an open position. This will cause all of the charge air to bypass the charge air cooler. Excessive charge air temperature at high engine loads is likely to lead to engine damage.